In a medium bowl, whisk together 3/4 cup flour, 1/2 cup brown sugar, ground cinnamon, and a pinch of salt. Pour in the melted butter and use a fork to toss the mixture together until generous, crumbly clumps form. Place the bowl in the refrigerator.

In the bowl of your stand mixer fitted with the paddle attachment, beat the softened butter, 1 cup brown sugar, and granulated sugar on medium-high speed for 3 minutes until pale and fluffy.

Scrape down the sides of the bowl. Add the room-temperature eggs one at a time, beating well after each addition, followed by 2 tsp vanilla extract.

In a separate bowl, whisk together 2 1/2 cups flour, cornstarch, baking powder, baking soda, and 1/2 tsp kosher salt. Turn the mixer to low speed and gradually add the dry ingredients to the wet mixture, stopping just as the last streaks of flour disappear.

Preheat your oven to 350°F (175°C) and line two large baking sheets with crinkled white parchment paper. Using a large cookie scoop, portion the dough into mounds. Press a shallow indentation into the top of each, then pack a generous handful of the chilled streusel onto the top of each cookie.

Bake for 11-13 minutes until the edges are just set and pale golden, while the center still looks slightly soft-baked. Allow to cool on the pan for 10 minutes before transferring to a wire rack to cool completely.

In a small bowl, whisk together the sifted powdered sugar, 1/2 tsp vanilla extract, and 2 tablespoons of heavy cream. Add more cream drop by drop if needed until you reach a thick, opaque consistency. Once cookies are perfectly cool, create a delicate zigzag drizzle crossing over the streusel and cookie edges.